Vinyl based cellulose reinforced composite

ABSTRACT

A cellulosic composite comprising: (a) at least one cellulosic material present in an amount in the range of from about 50% to about 75% by weight of the composite, (b) at least one polyvinyl chloride material present in an amount in the range of from about 25% to about 50% by weight of the composite, and (c) at least one polar thermosetting material present in an amount in the range of from about 0% to about 4% by weight of the composite is disclosed. An extruded article made form the cellulose composite and a method of making the cellulose composite are also disclosed.

This application claims the benefit of U.S. Provisional Application No.60/011,022, filed Feb. 1, 1996.

BACKGROUND OF THE INVENTION

The application relates generally to cellulose reinforced composites,and more particularly to vinyl based cellulose reinforced composites.

There is a very high demand for wood products. Although wood is arenewable resource, it takes many years for trees to mature.Consequently, the supply of wood suitable for use in construction isdecreasing. Therefore, there is a need to develop alternatives to theuse of wood in construction.

Wood replacement materials are known in the art. Wood scraps, such aswood meal, wood chips, and saw dust, have been mixed with differenttypes of materials, including plastics such as low and high densitypolyethylene, thermosetting resins, and epoxy resins. For example, U.S.Pat. Nos. 4,091,153, 4,686,251, 4,708,623, 5,055,247, 3,908,902,5,002,713, 5,087,400, and 5,151,238 relate to processes for producingwood replacement products.

Composites made from vinyl based thermoplastics, such as polyvinylchloride (PVC) chlorinated polyvinyl chloride (CPVC), and semi-rigidpolyvinyl chloride (S-RPVC), offer advantages over olefin basedcomposites. The advantages include improved weatherability and goodadhesion to the wood material without the need for adhesives or tielayers. However, vinyl based thermoplastics are generally more difficultto process than olefin based thermoplastics.

Therefore, there is a need for a vinyl based cellulose reinforcedcomposite which can be processed easily and without the need for complexdie arrangements.

DESCRIPTION OF THE INVENTION

In broadest terms, the present invention includes a cellulosic compositecomprising: (a) at least one cellulosic material present in an amount inthe range of from about 50% to about 75% by weight of the composite, (b)at least one polyvinyl chloride material present in an amount in therange of from about 25% to about 50% by weight of the composite, and (c)at least one polar thermosetting material present in an amount in therange of from about 0% to about 4% by weight of the composite.

It is preferred that the cellulosic material(s) is/are present in anamount in the range of from about 60% to about 70% by weight of thecomposite. It is also preferred that the cellulosic material(s) beselected from wood saw dust, seed husks, ground rice hulls, newspaper,kenaf, coconut shells, bagasse, corn cobs, and peanut shells, andmixtures thereof

It is preferred that the polyvinyl chloride material(s) be present in anamount in the range of from about 30% to about 40% by weight of thecomposite.

It is preferred that the thermosetting material(s) be present in anamount in the range of from about 0% to about 1% by weight of thecomposite.

The invention also includes an extruded article produced by extruding acellulosic composite of the present invention in its many embodiments asdescribed herein and as claimed.

The invention also includes a method of extruding a cellulosic compositein its many embodiments as described herein, the method comprising thesteps of: (1) extruding a cellulosic composite as described above and asclaimed, and (2) allowing the cellulosic composite to cure forsufficient time at sufficient temperature to form a solid extrudate.

The composite compound consists of rigid PVC dryblend compound, combinedwith relatively high loadings of cellulose reinforcement.

Optionally, thermosetting materials can be added to improve propertiessuch as moisture absorption and strength. Among the thermosettingmaterials which can be used are isocyanates, and phenolic and epoxyresins, and mixtures thereof.

    ______________________________________                                                                    Preferred Range                                   Ingredient    Range (by weight)                                                                           (by weight)                                       ______________________________________                                        Wood sawdust  50-75%        60-70%                                            PVC material  25-50%        30-40%                                            Thermosetting material                                                                      0-4%          0-1%                                              ______________________________________                                    

PVC has a relatively high melt viscosity coupled with a sensitivity tothermal degradation that can result in catastrophic breakdown of thepolymer in the manufacturing step of producing useful articles. It hasbeen found that the extremely high cellulose levels require aspecialized PVC material to facilitate extrusion into useful shapes.

The PVC material may include:

    ______________________________________                                                       Range (per 100                                                                           Preferred Range (per                                Ingredient     parts of resin)                                                                          100 parts of resin)                                 ______________________________________                                        PVC resin      100    parts   100    parts                                    (I.V. range of 0.6-1.0)                                                       Stabilizer     2-8    phr     5-7    phr                                      Lubricants     4-10   phr     6-8    phr                                      Process Aids   2-6    phr     3-5    phr                                      ______________________________________                                    

Tin stabilizers are preferred for environmental reasons; however, leadand metal soaps, such as barium, cadmium, and zinc, should worksimilarly.

Common commercial lubricants known in the plastics processing industry,both internal and external, can be used. Examples of lubricants whichcan be used include calcium stearate, esters, paraffin wax, and amidewax.

Process aids such as acrylic modifiers for PVC aid fusion of thecompound.

Additional components, for example foaming agents and compatibilizers,can be added if desired.

The PVC material can be made by mixing the PVC resin with thestabilizer, lubricants, and process aids in a high intensity mixer, suchas those made by Littleford Day Inc. or Henschel Mixers America Inc. Themechanically induced friction heats the ingredients to a temperaturebetween about 200° F. and 230° F. After mixing, the ingredients arecooled to ambient temperature.

The cellulose material should be dried to between about 0.5%-3% inmoisture content, preferably 1-2% moisture by weight.

The dried cellulose is combined with the PVC material and thethermosetting material, if any, in a low intensity mixer such as aribbon blender.

The mixture is preferably processed in a conical twin screwcouiiterrotating extruder with a vent. A force feed hopper (or"crammer") is preferred to feed the materials into the extruder,although other types of hoppers could be used.

The die design is streamlined with a compaction ratio of between about2:1 to 4:1. An extended die land provides the necessary back pressure toprovide a uniform melt, and compaction and shaping of the melt.

A vinyl based cellulose reinforced composite was made as follows. PVCresin was combined with 6 phr stabilizer, 7 phr lubricants, and 4 phrprocess aids in a high intensity mixer until a temperature ofapproximately 220° F. was obtained. The PVC material was then cooled toambient temperature. The wood flour was dried to a moisture content ofless than 2%. The dried wood flour (65%) was mixed with the PVC material(35%) in a ribbon blender for approximately 10 min. No thermosettingmaterials were added in this example.

The dry blend was then fed into a conical, counterrotating, twin screwextruder (Model CM80 by Cincinnati Milacron). The first two stages ofthe extruder were heated to about 380° F. The last two stages, which arelocated after the vent, were heated to about 350° F. The die temperaturewas also about 350° F. The screw temperature was about 360° F. Vacuumwas applied to the vent to further reduce the moisture in the extrudate.

A window profile was extruded without using a breaker plate to reducestagnant flow areas in the process where PVC compounds have a tendencyto thermally degrade. The breaker plate provides back pressure to theextruder to promote the necessary mixing for a homogenous melt deliveredto the die. Since the breaker plate was omitted to alleviatedegradation, the back pressure necessary to provide a uniform melt, andcompaction and shaping of the melt was accomplished within the die byproviding a 2:1 compression ratio coupled with an extended die land ofapproximately 6 inches.

The paint adhesion of the window profile was tested using ASTM D3359crosshatch tape pulls. The wood composites were abraded using 120 gritsandpaper. A latex primer from Finishes Unlimited was applied to theabraded surface with a brush and allowed to air dry for several days.The visual rating for paint adhesion for a high density polyethylenewood composite was 2B, while for the vinyl based wood composite therating improved to 3B.

Rectangular test bars measuring 1/4 inch by 1/2 inch and having 65% woodflour and 35% PVC material were made. The test bars were tested usingASTM D790. A modulus of 835,000 psi with a peak stress of 5,050 psi wasobtained. This compares favorably to a high density polyethylenecomposite with 65% by weight wood fibers which had a modulus of 540,000psi and 1,960 psi peak stress.

Aside from extruding the composition, it has somewhat surprisingly beenfound that the composition can be compression molded from a powdereddryblend. Flat plaques were made by placing the powdered dryblend in aheated press at a temperature of 350° F. for several minutes. This isunexpected in that compression, unlike extrusion, provides only pressureand heat without distributive shear.

The use of the vinyl base allows known weatherable thermoplastics suchas PVC, CPVC, and S-RPVC to be coextruded with good adhesion to the woodcomposite without the need for adhesives or tie layers. This is not thecase for olefinic based composites. In this way, aesthetics as well asoutdoor exposure resistance of the cellulose composite is enhanced forsuch applications as building products.

Resistance to ignition is expected to improve over an olefinic basedwood composite due to the halogen content of the vinyl.

The use of a vinyl based wood composite allows improved propertieswithout increased cost as compared to an olefin based wood composite.

Other embodiments of the invention will be apparent to those skilled inthe art from a consideration of the specification or practice of theinvention disclosed herein. It is intended that the specification andexamples be considered as exemplary only, with the true scope and spiritof the invention being indicated by the following claims.

What is claimed is:
 1. A cellulosic composite, said compositecomprising:(a) at least one cellulosic material present in an amount inthe range of from about 60% to about 70% by weight of said composite;(b) at least one polyvinyl chloride material present in an amount in therange of from about 30% to about 40% by weight of said composite, saidat least one polyvinyl chloride material comprised of at least onestabilizer present in an amount of about 2 to about 8 parts per 100parts of polyvinyl chloride resin, at least one lubricant present in anamount of about 4 to about 10 parts per 100 parts of polyvinyl chlorideresin, and at least one process aid present in an amount of about 2 toabout 6 parts per 100 parts of polyvinyl chloride resin; and (c) atleast one polar thermosetting material present in an amount in the rangeof from about 0% to about 4% by weight of said composite.
 2. Acellulosic composite according to claim 1, wherein said at least onecellulosic material is selected from wood saw dust, seed husks, groundrice hulls, newspaper, kenaf, coconut shells, bagasse, corn cobs, andpeanut shells, and mixtures thereof.
 3. A cellulosic composite accordingto claim 1, wherein said at least one thermosetting material is presentin an amount in the range of from about 0% to about 1% by weight of saidcomposite.
 4. An extruded article, said article produced by extruding acellulosic composite, said composite comprising:(a) at least onecellulosic material present in an amount in the range of from about 60%to about 70% by weight of said composite; (b) at least one polyvinylchloride material present in an amount in the range of from about 30% toabout 40% by weight of said composite, said at least one polyvinylchloride material comprised of at least one stabilizer present in anamount of about 2 to about 8 parts per 100 parts of polyvinyl chlorideresin, at least one lubricant present in an amount of about 4 to about10 parts per 100 parts of polyvinyl chloride resin, and at least oneprocess aid present in an amount of about 2 to about 6 parts per 100parts of polyvinyl chloride resin; and (c) at least one polarthermosetting material present in an amount in the range of from about0% to about 4% by weight of said composite.
 5. An extruded articleaccording to claim 4, wherein said at least one cellulosic material isselected from wood saw dust, seed husks, ground rice hulls, newspaper,kenaf, coconut shells, bagasse, corn cobs, and peanut shells, andmixtures thereof.
 6. An extruded article according to claim 4, whereinsaid at least one thermosetting material is present in an amount in therange of from about 0% to about 1% by weight of said composite.